Is it possible to switch users in Debian without entering a password, as in Ubuntu Maverick?
I already tried adding a nopasswdlogin group but it did not work, even though the "don't ask for password on login" entry in the login manager is no longer greyed out. Replacing gdm3 with gdm also did not work.

I certainly hope not. It goes against all the principles of safe HEX.

Update: I find that if I add the line

auth sufficient pam_succeed_if.so user ingroup nopasswdlogin

to /etc/pam.d/gdm [not gdm3] I can log in to my secondary account without password, but I still get the login screen - isn't the whole point of fast user switching to avoid this? This seems to be a bug in indicator-applet-session (quite an old one apparently; I am not the only one having problems with it). The nopasswdlogin group does not exist by default, but I created it. And I don't see how this should be a security risk - this account is a desktop account without sudo rights, and belongs to me; no one else has access to my computer - unless they break into my apartment, but then passwords would not be too much use anyway... (The password exists, but is not asked at login. This is no different from automatic login).

I admit though, this problem is not too important.

I wonder why most people think that nobody has access to their machines, when they connect their machines to the net.

Some users block incomming connections on the firewall or just do not start services like ssh or ftp and they can afford to use automatic login. There is always a battle between comfort and security. Now I understand why some of these programs disallow loging for users without passwords by default.

Okay, I'll take the bait. I have no sensitive information on my computer - I use Linux for experimenting and learning, and I have already learned a bit through Debian (see my sudo thread - might be interesting for Ubuntu too). As for the indicator applet and Ubuntu-style session switching, there does not seem to be any solution, so we might as well close this thread.